Electroluminescence display panel, image display, and method for manufacturing them

ABSTRACT

The present invention provides the following methods and displays. A method for manufacturing an EL display panel, having the step of forming a light-emitting layer by irradiating light on a photothermal conversion layer through a transparent base member while a dye layer of a transfer member having the transparent base member, the photothermal conversion layer and this fluorescent dye layer is kept in close contact with an object to which the dye is to be transferred, the transparent base member, the photothermal conversion layer and the transfer member being laminated in this order, so that the dye can be transferred to the object. An EL display panel produced according to this method, an image display having this panel, and a method for manufacturing the image display.

TECHNICAL FIELD

The present invention relates to organic electroluminescence (EL)elements, an image display and a method for manufacturing them.

BACKGROUND ART

The three primary colors, RGB (Red, Green and Blue) of an image displayusing organic EL elements have been produced by a method of evaporatingcolor materials through a metal mask (hereafter, called the maskevaporation method) as described in “9^(th) International workshop onInorganic and organic electroluminescence, p. 137 (1998)” or by a methodof applying the ink jet printing (hereafter, called the ink jet method)as described in “Extended Abstract of EL98, 147 (1998)”. However, it isdifficult to produce large-area and high-resolution screens for futuredemand by these conventional methods.

For example, in the mask evaporation method it is hard to make a thinmask of several tens of μm in close contact with a large substratewithout wrinkle or folds and to remove the effect of thermal expansionin the evaporation of metal electrodes. Therefore, it is difficult torealize large area, high-resolution screens. In addition, the ink jetmethod is inappropriate for printing sufficiently wide andhigh-resolution light-emitting regions because of its lowdeposition-positioning precision.

Thus, as a method capable of solving these problems, there has beenproposed a method of transferring dye materials onto a substrate so thatthe transfer layer and the transferred layer can be kept in closecontact with each other without use of liquid solution. In this method,as described in “Society of Information Display '00, p. 1080 (2000)”, apattern of three primaries RGB is formed by screen-printing on atransfer substrate from which the dye materials are to be transferred,and the three-primary materials are thermally transferred to thetransferred substrate at a time.

In this transfer technique, however, a dye pattern is formed by thescreen printing method using a solution, and thus it is difficult toproduce a large-area and high-resolution pattern that is to betransferred. In addition, since three-color dye materials aretransferred at a time, a long transfer time of tens of minutes must betaken in order for the transfer speeds of the color materials to beadjusted.

DISCLOSURE OF THE INVENTION

It is an object of the invention to provide a large-area andhigh-resolution EL device, an image display having this device, and amethod for manufacturing them.

According to this invention, in order to achieve this object, there isprovided a method for manufacturing an EL display panel, this methodhaving steps in which light is irradiated on a photothermal conversionlayer through a transparent base member while a fluorescent dye layer ofa transfer member that has the transparent base member, the photothermalconversion layer (a layer that absorbs light and generates heat) andthis dye layer stacked n this order is kept in close contact with thebody to which the dye is to be transferred so that the fluorescent dyecan be transferred to the body, thus forming the light-emitting layer.

The transparent base member may be anything, for example, a glass plateas long as irradiation light for transfer can be transmitted through it.In addition, the irradiation light used here is desired to be laser beamthat can be irradiated only on a necessary portion (namely, an area inwhich the pixels are built up). It is also desired possible that onlythe necessary region is exposed to light by irradiating light through aphotomask.

According to the invention, since only the dye in the exposed region istransferred, the dye pattern of materials to be transferred is notnecessarily formed at a strictly precise location. Therefore, thisinvention is effective to produce a high-resolution and large-areadisplay panel.

Moreover, according to the invention, the three primaries RGB can beseparately transferred, and thus it is not necessary to adjust thetransfer speeds of the light-emitting materials. Also, since the threedifferent color dyes can be transferred from different base members inaddition to the merit that the light-emitting layer can be formed bytransfer, the number of manufacturing processes can be reduced by one ascompared with the conventional method in which the three color dyes aretransferred at a time.

In this invention, the photothermal conversion layer for absorbing lightand generating heat is provided in the transfer member as a foundationlayer for the fluorescent dyes. Therefore, according to the invention,since the irradiated light can be converted into heat with goodefficiency, the dyes can be transferred in a short time.

In addition, according to the invention, there is provided a method formanufacturing an EL display panel, this method having the steps ofproducing a first electrode on a substrate, producing a partition wallon the electrode, producing a first charge transport layer on theelectrode, and transferring the fluorescent dyes on the surface of thecharge transport layer, the height of the top of the partition wallformed by the step of producing the partition wall being lower than thatof the top of the light-emitting layer. In this specification, except asotherwise noted, the lamination direction of the panel is assumed to bevertical, and the substrate side to be bottom. In addition, the heightsof the tops of the partition wall and charge-transport layer are assumedto measure from the substrate.

Moreover, according to this invention, there is provided an EL displaypanel having a substrate, and a first electrode, a plurality oflight-emitting portions that emit light when excited by voltageapplication, a second electrode, and a partition wall for separating theadjacent light-emitting portions which are laminated on the substrate inthis order, the light-emitting portions having at least a first chargetransport layer and a light-emitting layer laminated in this order fromthe substrate side, and the height of the top of the partition wallbeing lower than that of the top of the light-emitting layer.

Since the height of the top of the partition wall is kept lower thanthat of the first charge transport layer, the light-emitting regionsmatched with the size of the light-emitting portions can be producedwithout the effect of the beam diameter of the irradiation light wheneach dye is transferred to necessary locations by light irradiation. Thetop of the partition wall is desirably water-repellent. For example, afluorine compound, when included, can provide high water-repellency.Here, the water-repellency means that the contact angle to the solutionfor producing the charge transport layer is higher than 50°.

The light-emitting layer in this invention is desirably the diffusionlayer of fluorescent dye formed on the second electrode side of thefirst charge-transport layer. Here, the diffusion layer is the layerformed by diffusing fluorescent dye into the charge transport substancethat constitutes the first charge-transport layer. The dye content canbe properly determined according to need, but defined to be, forexample, 0.1 weight % or more contained in the upper portion of thefirst charge transport layer.

Moreover, since the light-emitting efficiency is raised by increasingthe charge confining effect, it is desirable to provide a secondcharge-transport layer between the light-emitting layer and the secondelectrode.

In addition, according to the invention, there is provided an EL displaypanel having a substrate, and a first electrode, a plurality oflight-emitting portions that emit light when excited by voltageapplication, a second electrode, and a partition wall for separating theadjacent light-emitting portions which are laminated on this substratein this order, the top end of the side of the partition wall made incontact with the light-emitting portions being covered by at least anylayer of the light-emitting portions and/or an insulating layer.Therefore, the cathodes can be prevented from short circuit.

In the EL display panels of the present invention, the top surface ofthe light-emitting portions is desirably a curved surface to be convextoward the second electrode. By forming the light-emitting portions insuch a shape, it is possible to increase the light-emitting efficiency.

Also, according to the invention, there are provided an image displayhaving the above EL display panel of the invention, and a method formanufacturing it.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pattern diagram of a pixel of the image display in theembodiment 1.

FIG. 2 is a cross-sectional diagram taken along a line A-A′ in the imagedisplay of the embodiment shown in FIG. 1.

FIG. 3 is a circuit diagram of the pixel of the image display in theembodiment 1.

FIG. 4 is a circuit diagram of the whole display portion of the imagedisplay in the embodiment 1.

FIG. 5 is a circuit diagram of the whole image display in the embodiment1.

FIGS. 6˜12 are process flow diagrams of a method for manufacturing theimage display in the embodiment 1.

FIG. 13 is a partial cross-sectional diagram of a pixel of the imagedisplay in the embodiment 2.

FIG. 14 is a partial cross-sectional diagram of a pixel of the imagedisplay in the embodiment 3.

FIG. 15 is a partial cross-sectional diagram of a pixel of the imagedisplay in the embodiment 4.

FIG. 16 is a partial cross-sectional diagram of a pixel of the imagedisplay in the embodiment 5.

FIG. 17 is a partial cross-sectional diagram of a pixel of the imagedisplay in the embodiment 6.

FIG. 18 is a diagram to which reference is made in explaining thetransfer process in the embodiment 7.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the invention will be described with reference to thedrawings. However, this invention is not limited to these embodiments.In addition, in the following embodiments, the present invention isapplied to the organic EL device having the light-emitting layers ofthree colors RGB, but is not limited to the device. For example, theinvention can be applied to a device having a hole blocking layer or adevice having a green-light emission layer/electron transporting layer,a red-light emission layer and a blue-light emission layer.

Embodiment 1

A. Construction of Pixel

The pixels of the display panel of the image display produced in thisembodiment have, as shown in FIG. 2, a wiring substrate 60, organic ELelements 7 and a partition wall 11 formed on the surface of thesubstrate. The wiring substrate has a glass substrate 18,electrode/wiring lines 1˜3, 2 a, and interlaminar insulating layers 17,19.

FIG. 1 is the top view of this pixel. For easy viewing, we omitted theillustration of the insulating layers in FIG. 1. FIG. 2 is across-sectional view taken along the line A-A′ in FIG. 1. As illustratedin FIG. 1, the video signal electrode 1, scanning signal electrode 2,common potential electrode 3 and current supplying electrode 4 frame anactive matrix. In addition, a switching transistor 5, a drivingtransistor 6 and a capacitor 12 are provided for energizing the organicEL element 7 in each matrix element.

The organic EL element 7, as shown in FIG. 2, has an anode 8 connectedto the driving transistor 6, a charge-transport layer 9, alight-emitting layer 10, and a cathode. The cathode corresponds to thecurrent supplying electrode 4. The top of the charge-transport layer 9is higher than that of the partition wall 11.

FIG. 3 is a circuit arrangement of one pixel of the image display inthis embodiment. As illustrated, the switching transistor 5 is turned onwhen a scanning signal is applied to the scanning signal electrode 2,and as a result, the potential of the video signal electrode 1 is storedin the capacitor 12 and transmitted to the driving transistor 6. Thispotential determines the voltage to be applied to the organic EL element7. The light-emitting layer 10 is energized to emit light by thecurrents flowing from the common potential electrode 3 and currentsupplying line 4 due to the potential. The image display of thisembodiment utilizes the light emission from this light-emitting layer 10to display images.

FIG. 4 is a circuit diagram of the whole display portion. The circuitarrangement of each pixel shown in FIG. 3 is connected as one element ofthe matrix to the n video signal electrodes 1 and n scanning signalelectrodes 2, thus constituting the display.

FIG. 5 shows the whole circuit arrangement including driving circuits.The scanning signal is supplied from a scanning signal source 13 to thescanning signal electrodes 2. The video signal is supplied from a videosignal source 14 to the video signal electrodes 1. The current from acurrent supplying source 15 is supplied to the current supplyingelectrode 4. The charges from a common potential supplying source 16 aresupplied to the common potential electrodes 3. In addition, even anon-photosensitive material may be similarly used if it can be patternedby using a resist.

B. Manufacturing Process

The manufacturing process for the partition wall 11 and organic ELelement 7 in this embodiment will be described below.

(1) Production of Lower Electrode and Partition Wall 11

First, the anode 8 was formed on the surface of wiring substrate 60(FIG. 6), and further the partition wall 11 of a predetermined patternwas formed over the anode (FIG. 7). This partition wall 11 can be formedby using the normal photolithography. The material for the partitionwall 11 may be a photosensitive material such as acrylic- orpolyimide-based material.

In addition, even a non-photosensitive material may be similarly used ifit can be patterned by using a resist.

This partition wall material may be the conventionally used material.However, it is desirable to finish the top 11 a of the partition wall tohave water repellency, thus further suppressing the transfer to thepartition wall 11, and making the peeling after transfer easy. In orderto give this top 11 a of partition wall the water repellency, it isnecessary to, for example, make a plasma treatment using CF₄ gas.Moreover, the partition wall 11 may be formed by using a water-repellentmaterial containing fluorine compound. Fluorine atoms to the surface ofpartition wall 11 can cause the top of the partition wall to exhibithigh water repellency.

(2) Deposition of First Charge Transport Layer 9

Then, the solution containing the charge transport material was coatedon the anode 8, and dried to form the charge transport layer 9 (electrontransport layer), thus completing the laminated body 80 (FIG. 8). Inthis embodiment, the charge transport material used here was a mixtureof polyvinyl carbazole expressed by the following chemical formula (1)and Bu-PBD expressed by the following chemical formula (2), of which themixture ratio is 3:1.

Other charge transport materials may be used; for example, a polymerhaving triphenylamine bone structure, a polymer having dispersed thereina low-molecular-based charge transport material such astriphenyldiamine, polyfluorene-based polymer as conjugated polymer thatalso functions as a light-emitting layer,polyparapolyphenylenevinylene-based polymer or copolymers of them.

This charge-transport layer 9 may be formed by coating the solutioncontaining the charge transport material, and then removing theunnecessary charge transport material from the partition wall 11 bylaser ablation or may be formed by the normal photolithography.

(3) Deposition of Light-Emitting Layer 10

Subsequently, a photothermal conversion layer 20 and a dye layer 21containing a blue dye were laminated on a transfer base (glass plate)22, thus producing a transfer member (blue) 90. This transfer member 90was pressed against the laminated body 80 so that the dye layer 21 couldbe made in contact with the top of the charge-transport layer 9 (FIG.9). Then, laser light 23 was irradiated on a predetermined area (wherethe blue pixels are formed) (FIG. 10).

The heat generated from the exposed photothermal conversion layer 20acts on the dye layer 21 so that the fluorescent dye contained in thedye layer 21 of the transfer member 90 that is made in contact with thecharge transport layer 9 can be thermally diffused into the chargetransport layer 9 to form the light-emitting layer 10 (bluelight-emitting pattern) only on the top of the charge transport layer 9(FIG. 11). In addition, since the dye is diffused only into the top ofthe charge transport layer 9 that is made in contact with the dye layer,a high-resolution light-emitting layer can be formed not depending onthe shape of the laser beam.

In this embodiment, a polymer film containing chromium oxide was usedfor the photothermal conversion layer 20. Other photothermal conversionmaterials that can be used here may be organic black pigments such asperylene derivatives, metallic compounds such as TbFeCo, black alumina,and carbon black.

In addition, continuous-oscillation Nd:YAG laser was used for the laserbeam. The laser scan speed was 128 m/sec. The output was 3W, and thebeam diameter was 40 μm (1/e²). The laser used here is not limited tothe Nd:YAG laser, but may be a semiconductor laser or DPSS laser.

Then, this transfer process (FIGS. 9˜11) was performed for each color ofgreen and red to form the light-emitting layers 10 of RGB pixels thathave three-color, RGB light-emitting patterns.

(4) Deposition of Upper Electrode

Subsequently, the power-supplying electrode (cathode) 4 was depositedover the substrate (FIG. 12). While Mg:Ag alloy was used for the cathodematerial in this embodiment, Al:Li alloy or LiF/Al lamination film maybe used. In this embodiment, the RGB pixels having a pixel pitch of0.127 mm×0.042 mm could be uniformly formed in a stripe shape.

(5) Assembly of Image Display

Thus, we produced the EL display panel having the organic EL elements.Finally, we normally assembled the image display by using this panel.

Embodiment 2

FIG. 13 is a cross-sectional view of the pixel of the image-displayproduced in this embodiment. In this embodiment, although only a singlecharge-transport layer was provided in the embodiment 1, the secondcharge-transport layer 9 (, or electron layer 9 b) containing the chargetransport substance was provided by after the formation oflight-emitting layer 10 but before the deposition of cathode 4.

The electron transporting layer 9 b as the second charge-transport layer9 acts to increase the charge confining effect in the image display ofthis embodiment, and thus making it possible to raise the light-emittingefficiency. Moreover, since the top of the interface between thepartition wall 11 and the charge transport layer 9 can be covered bythis second charge transport layer 9, it is possible to prevent theshort circuit from occurring when the cathode 4 is deposited.

Embodiment 3

FIG. 14 is a cross-sectional view of the pixel of the image displayproduced in this embodiment. In this embodiment, the image display wasproduced in the same way as in the embodiment 1. However, in the process(2) of embodiment 1, the charge-transport layer 9 was formed to coverthe top of the side 11 b of the partition wall 11. This structure can bebuilt up by photolithography or laser abrasion.

The structure in which the top of the side of the partition wall 11 iscovered by the charge-transport layer 9 is desirable because shortcircuit can be prevented from occurring after the cathode 4 isdeposited.

Embodiment 4

FIG. 15 is a cross-sectional view of the pixel of the image displayproduced in this embodiment. In this embodiment, too, the image displaywas produced in the same way as in the embodiment 1. However, aninsulating layer 28 was formed on the surfaces of the outer edges of thepartition wall 11 and light-emitting layer 10, after the light-emittinglayer 10 was formed but before the cathode 4 was deposited, so that itcan cover the top of the side 11 b of the partition wall 11. Thestructure of this embodiment is also such that the top of the side ofthe partition wall 11 is covered by the insulating layer 28, as is thestructure of the embodiment 3. Thus, the short circuit can be preventedafter the formation of the cathode 4. A buffer layer may be provided inplace of the insulating layer 28.

Embodiment 5

In this embodiment, the image display was produced in the same way as inthe embodiment 1 except that the top of the charge transport layer 9formed in the process (2) was formed in a dome shape shown in FIG. 16,or the top was curved to be convex upward. This domed shape can beachieved by depositing the partition wall 11 with a water-repellentmaterial and then coating the solution of charge transport material toform the charge-transport layer 9. The light-emitting efficiency of thedisplay of this embodiment was about 10% higher than that of theembodiment 1.

The domed shape of the top of the charge-transport layer 9 can berealized by depositing a domed insulating layer under the anode 8.

Embodiment 6

In this embodiment, the image display was produced in the same way as inthe embodiment 2. However, as shown in FIG. 17, the lower electrode ofthe organic EL element formed in the process (1) was formed not as theanode 8 but as the cathode 4. In the process (4), the upper electrodewas formed not as the cathode 4 but as the anode 8. In addition, whenthe charge-transport layer 9 was formed in the process (2), the electrontransport layer 9 b was produced by using an electron transportsubstance. When the charge-transport layer was deposited after theformation of the light-emitting layer 10 of process (3), the holetransporting layer 9 a was formed by using a hole transportingsubstance.

Thus, in the image display of this embodiment, the light-emitting regioncould be made wider than that of the embodiment 2, and the powerefficiency could be more increased.

Embodiment 7

While the photothermal conversion layer 20 at the locationscorresponding to the light-emitting pattern was exposed to the scanninglaser beam in the embodiment 1, light 23 a was irradiated through aphotomask 27 in this embodiment as shown in FIG. 18.

By using the photomask as in this embodiment, it is possible to exposeat a time without the scanning light, and therefore the light-emittinglayer 10 can be formed by transfer in a short time. In the embodiment 1,a time of about 100 seconds was taken for the substrate having a size of830 mm×650 mm to be exposed to light. On the other hand, in thisembodiment, the substrate of that size could be exposed in a shortertime of 60 seconds.

INDUSTRIAL APPLICABILITY

As described above, this invention can provide a high-resolution andlarge-area organic EL display panel. In addition, a large-screen andhigh-resolution image display can be easily produced by using thisorganic EL display panel.

1. An electroluminescence display panel comprising: a substrate a firstelectrode; a plurality of light-emitting portions that emit light when avoltage is applied thereto; a second electrode; an insulating layer; anda partition wall for separating the adjacent ones of said light-emittingportions, wherein said first electrode, said llight-emitting portions,said insulating layer, and said second electrode are disposed on saidsubstrate in this order, said light-emitting portions having at least afirst charge transport layer and a light-emitting layer disposed in thisorder on said substrate, and the height of the top of said partitionwall being lower than that of said light-emitting layer; wherein saidlight emitting layers being sandwiched with said first charge transportlayer and a second charge transport layer in such a manner that onecharge transport layer is formed to cover said light-emitting layers andsaid partition walls.
 2. An electroluminescence display panel accordingto claim 1, wherein said top of said partition wall is water-repellent.3. An electroluminescence display panel according to claim 1, whereinsaid top of said partition wall contains fluorine compound.
 4. Anelectroluminescence display panel according to claim 1, wherein saidlight-emitting layer is a diffusion layer of fluorescent dye formed onthe second electrode side of said first charge transport layer.